The present invention relates to a technical field of a display device such as a liquid crystal device, and more particularly to a technical field of a transflective monochrome or color display device capable of displaying while switching between a reflective display and a transmissive display, an electronic apparatus using such a display device, and a light guide plate suitable for use in such a display device.
So far, reflective liquid crystal devices, because of its small power consumption, have come into widespread use as additional sections of portable units, apparatus and others, while there is a problem which arises with the reflective liquid crystal devices, however, in that, because a display is made visible through the use of the external light, the display is unreadable in the dark. For this reason, a transflective liquid crystal device, in which a display is made visible through the use of the external light in the light as in common reflective liquid crystal devices but through the use of an internal light source in the dark, has been proposed as exemplified by Japanese Unexamined Utility Model Publication No. 57-049271. Particularly, in connection with a transflective liquid crystal device utilizing a polarization axis variable means for rotating a polarization axis of a TN (Twisted Nematic) liquid crystal, a STN (Super-Twisted Nematic) liquid crystal or the like, this applicant has proposed a transflective display device using, as a means to better the brightness in the reflective display, a polarized light splitter which causes the reflection of a linearly polarized light component running in a predetermined direction while allowing the transmission of a linearly polarized light component advancing in a direction perpendicular thereto (Japanese Patent Application No. 8-245346). Referring to FIG. 22, a description will be made hereinbelow of a transflective display device using this polarized light splitter.
In FIG. 22, a TN liquid crystal panel is composed of an upper polarizer 5130, an upper glass substrate 5302, a lower glass substrate 5304, a polarized light splitter 5160, a semipermeable light absorbing layer 5307 and a light source 5210. In the illustration, a TN liquid crystal, placed between the upper glass substrate 5302 and the lower glass substrate 5304, is divided into a voltage non-applied area 5120 and a voltage applied area 5110.
First, a description will be given hereinbelow of achromatic display of a reflective display. Incident light from the exterior of the display device, indicated as an optical path 5601, turns through the upper polarizer 5130 to linearly polarized light in a direction parallel with the paper surface, and then form a linearly polarized light component in a direction perpendicular to the paper surface with its polarizing direction being twisted by 90xc2x0 in the voltage non-applied section 5120 of the TN liquid crystal panel, and further is reflected on the polarized light splitter 5160 in a state of the same linearly polarized light in the direction perpendicular to the paper surface, and again undergoes a twist of 90xc2x0 in its polarizing direction in the voltage non-applied section 5120 of the TN liquid crystal panel to develop into a linearly polarized light component in a direction parallel with the paper surface, finally going out of the upper polarizer 5130. Accordingly, no application of a voltage to the TN liquid crystal panel makes a white display. Thus, the white display light is light reflected on the polarized light splitter 5160, which produces a brighter display than a conventional transflective display device. The light indicated by an optical path 5603 forms linearly polarized light in a direction parallel with the paper surface due to the upper polarizer 5130, and advances with its polarizing direction remaining intact even in the voltage applied section 5110 of the TN liquid crystal panel and with it remaining the same linearly polarized light in the direction parallel with the paper surface, and further transmits with its polarizing direction being also kept intact even in the polarized light splitter 5160, thereafter being absorbed by the semipermeable light absorbing layer 5307 to produce a black display.
Secondly, a description will be given hereinbelow of achromatic display of a transmissive display. Light indicated by an optical path 5602 passes through an opening section made in the semipermeable light absorbing layer 5307 and turns to linearly polarized light in a direction parallel with the paper surface in the polarized light splitter 5160, and then undergoes a twist of 90xc2x0 in its polarizing direction in the voltage non-applied section 5120 of the TN liquid crystal panel to form linearly polarized light perpendicular to the paper surface, thereafter absorbed in the upper polarizer 5130 to produce a black display. Light indicated by an optical path 5604 comes in through an opening section made in the semipermeable light absorbing layer 5307 turns through the polarized light splitter 5160 to form a linearly polarized light in a direction parallel with the paper surface and passes through the upper polarizer 5130 with its polarizing direction being kept intact even in the voltage applied section 5110 of the TN liquid crystal panel and with it remaining the same linearly polarized light parallel with the paper surface, thus providing a white display.
As described above, the transflective display device (Japanese Patent Application No. 8-245346) this applicant has proposed can accomplish more proper switching between a reflective display and a transmissive display in accordance with ON/OFF of a light source, which provides a relatively bright reflective display.
On the other hand, with the recent progress of portable equipment (portable telephones, PDAS, watches) or OA equipment, a request has existed for coloring in liquid crystal display, and even a requirement for coloring has occurred to equipment using such a transflective liquid crystal device. In general, a color filter is put to use for coloring of display on a liquid crystal device. However, the color filter absorbs light so that the display tends to be dark. Therefore, in order to enhance the utilization efficiency of light, there has sometimes been employed a mode (which will be referred to hereinafter as an xe2x80x9cSPDxe2x80x9d) in which a polarizer is provided only on the visible side of the liquid crystal device and a reflecting layer is provided on an inner surface of a liquid crystal substrate. In the case of this SPD mode, only one polarizer can improve the utilization efficiency of light. Additionally, for realizing a transflective liquid crystal device with the SPD mode, a hole(s) is made in a portion of the reflecting layer or the reflecting layer is made relatively thin; whereupon, the reflecting layer has a permeable function to enable a transmissive display.
However, the use of the polarized light splitter shown in FIG. 22 causes a positive-negative reversal phenomenon due to a difference between incidence on the polarized light splitter from the upper side and incidence from the lower side. Thus, the mode of the positive-negative reversal between a transmissive display and a reflective display creates a problem in that it is unsuitable for the display device depending on the applications of the display device, or is impracticable. Additionally, because of the use of the semipermeable light absorbing layer, the utilization efficiency of light drops, particularly at the transmissive display, it becomes dark.
On the other hand, with the transflective liquid crystal disclosed in Japanese Unexamined Utility Model Publication No. 57-049271, since a thick transparent substrate of a liquid crystal panel is interposed between a liquid crystal layer and a transflective layer, double image or display bleeding occurs due to parallax, particularly for coloring, the color filter cannot exhibit sufficient color development.
Furthermore, the SPD mode requires lowering reflectance of a reflecting layer, which leads to a dark reflective display. Conversely, if the reflectance of the reflecting layer is increased in order to brighten the reflective display, then a dark transmission display occurs, which requires the enhancement of back light luminance. As described above, with the conventional transflective color display device, extreme difficulty is encountered in accomplishing a bright good-looking color display not only at the reflective display and but also at the transmissive display.
Accordingly, the present invention has been developed in consideration of the above-mentioned problems, and it is an object of the invention to provide, of transflective display devices using a polarization axis variable means, a transflective display device capable of preventing the positive-negative reversal between a reflective display relying on the external light and a transmissive display relying on lighting by a light source and further of achieving bright good-looking monochrome or color display, and further to provide an electronic apparatus using such a display device and a light guider suitable for use in such a display device.
The foregoing object of this invention is achievable by a display device comprising a liquid crystal panel in which a transmissive polarization axis is variable, first and second polarized light splitting plates located on both sides of the liquid crystal panel to interpose the liquid crystal panel therebetween, a reflecting layer located on the opposite side to the liquid crystal panel with respect to the second polarized light splitting plate, a light source, a light guider interposed between the second polarized light splitting plate and the reflecting layer for guiding light from the light source so that the light is incident through the second polarized light splitting plate on the liquid crystal panel and further for allowing transmission of light from the second polarized light splitting plate side and transmission of light from the reflecting layer side, and a front scatterplate interposed between the liquid crystal panel and the reflecting layer for scattering forwardly each of light from the reflecting layer side toward the liquid crystal panel side and light from the liquid crystal panel side toward the reflecting layer side.
With the first display device according to this invention, in the reflective display, the external light incident from the first polarized light splitting plate (for example, a polarizer or a reflecting polarizer) passes through the first polarized light splitting plate, the liquid crystal panel, the second polarized light splitting plate (for example, a polarizer or a reflecting polarizer), the front scatterplate and the light guider, and is then reflected on the reflecting plate to be outputted from the first polarized light splitting plate. At this time, the light (for example, a linearly polarized light) polarized through the first polarized light splitting plate, the liquid crystal panel and the second polarized light splitting plate is scattered forwardly when passing through the front scatterplate to form white scattering light which in turn, is reflected on the reflecting layer. This reflected light is further scattered forwardly through the front scatterplate and, as white scattering light, passes through the second polarized light splitting plate, the liquid crystal panel and the first polarized light splitting plate to be outputted as the re-polarized light from the first polarized light splitting plate side. In this way, since the polarized state of the external light (reflected light) reflected on the reflecting layer and further scattered forwardly by the front scatterplate varies through the second polarized light splitting plate, the liquid crystal panel and the first polarized light splitting plate so that the reflective display takes place, when viewed from the first polarized light splitting plate side, the scattering plane of the front scatterplate on which the reflected light is scattered forwardly look as if it is at the reflecting position. Accordingly, even if the distance from the liquid crystal panel to the reflecting layer is prolonged, neither double image nor bleeding in display occurs due to parallax. In this invention, the term xe2x80x9cforward scatteringxe2x80x9d signifies that the quantity of light scattered forwardly is larger than the quantity of light scattered rearwardly with respect to the advancing direction of incident light.
On the other hand, in the transmissive display, the light source light emitted from the light source and guided by the light guider varies in its polarized state through the second polarized light splitting plate, the liquid crystal panel and the first polarized light splitting plate, thereby carrying out the display. This enables a bright display through the use of the light source light in a dark place.
In a mode of the first display device according to this invention, the front scatterplate is put between the liquid crystal panel and the light guider.
According to this mode, in the transmissive display, the light source light emitted from the light source and guided by the light guider is scattered forwardly by the front scatterplate and is incident on the second polarized light splitting plate as white scattering light so that a display is made in a state where its polarized state varies through the second polarized light splitting plate, the liquid crystal panel and the first polarized light splitting plate. Particularly, as compared with the case in which the light guider is interposed between the front scatterplate and the liquid crystal panel, the distance between the front scatterplate and the liquid crystal panel is shorter; whereupon, the scattering plane of the front scatterplate which looks like the reflecting position in the reflective display in connection with that shortness approaches the liquid crystal panel. In consequence, the double image or display bleeding due to the parallax caused by the distance between the front scatterplate and the liquid crystal panel is reducible. Additionally, since the reflected light of the external light is developed into white scattering light in the front scatterplate, shadow on the reflecting layer occurring due to the parallax stemming from the light guider reduces in a dark section displayed by being absorbed in the second polarized light splitting plate.
In another mode of the first display device according to this invention, the optical anisotropy in the light guider is so low that it hardly has influence on display chrominance non-uniformity in the display device.
According to this mode, since the light guider is optically close to the isotropy, the corresponding optical anisotropy is high so that colored appearance of display or occurrence of chrominance non-uniformity is avoidable. Additionally, for prevention of such chrominance non-uniformity, if the optical scattering of the reflecting layer or the front scatterplate is made to step up, then the occurrence of a dark display is also avoidable.
In a further mode of the first display device according to this invention, in the light guider, the optical axis direction is constant.
According to this mode, contrary to the aforesaid mode in which the optical anisotropy of the light guider is low, the light guider has an optical anisotropy and the optical axis direction is constant, that is, it has a rule such as uniaxial or biaxial, which can eliminate the chrominance non-uniformity and enhance the contrast while enlarging the angle of field in display.
In a further mode of the first display device according to this invention, a third polarized light splitting plate is additionally provided between the second polarized light splitting plate and the light guider. In this case, the aforesaid first polarized light splitting plate acts as a polarized light splitting plate which transmits, absorbs or reflects incident light in accordance with its polarized light component, while the aforesaid second polarized light splitting plate serves as a polarized light splitting plate which transmits, absorbs or reflects incident light in accordance with its polarized light component, and even the aforesaid third polarized light splitting plate functions as a polarized light splitting plate which transmits or reflects incident light in accordance with its polarized light component, with the direction of the polarization axis of the second polarized light splitting plate coinciding approximately with the direction of the polarization axis of the third polarized light splitting plate.
According to this mode, each of the first and second polarized light splitting plates are made, for example, from a polarizer. Additionally, the third polarized light splitting plate, for example composed of a reflecting polarizer, accepts the transmission of a linearly polarized light component of the incident light from the second polarized light splitting plate, assuming a direction coinciding approximately with the direction of the polarization axis of the second polarized light splitting plate, to the light guider side to output a portion of the incident light from the light guider to the second polarized light splitting plate side while reflecting the remaining portion thereof to the light guider side, thereby accomplishing polarization separation. Thus, it is possible to effectively use almost all light existing between the light guider and the reflecting layer, so bright image is achievable not only in the reflective display but also in the transmissive display. In this case, the xe2x80x9cthe direction of the transmission axes coincide approximatelyxe2x80x9d signifies that the angle made between the direction of these transmission axes is in the range of 0xc2x0 to 40xc2x0, preferably in the range of 0xc2x0 to 15xc2x0. Particularly, as the angle made between these polarization axis directions increases, the transmissive display becomes darker.
In this mode, it is also possible that the third polarized light splitting plate is a polarized light splitting plate which reflects, of the incident light, a linearly polarized light component in a direction substantially perpendicular to the direction of the polarization axis of the third polarized light splitting plate.
In this construction, owing to the polarization separation in the third polarized light splitting plate made from a reflecting polarizer, it is possible to effectively use almost all light existing between the light guider and the reflecting layer, so extremely bright reflective and transmissive displays are attainable.
In this case, it is also appropriate that the third polarized light splitting plate is a laminated member produced by piling up a plurality of layers closely, and the refractive indexes of the plurality of layers are equal to each other between adjacent layers in one predetermined direction while being different from each other in another direction perpendicular to that one predetermined direction.
With this construction, in the third polarized light splitting plate composed of a reflecting polarizer, of light incident on one main surface of the third polarized light splitting plate from the piling-up, a linearly polarized light component in one predetermined direction reaches the other main surface on the opposite side in the state of the linearly polarized light component in that one predetermined direction, while a linearly polarized light component in another predetermined direction perpendicular to that one predetermined direction is reflected thereon as the linearly polarized light component. Furthermore, of light incident on the other main surface of the third polarized light splitting plate from the piling-up direction, a linearly polarized light component in that one predetermined direction arrives at the opposite side of one main surface side in a state of the linearly polarized light component in that one predetermined direction, while a linearly polarized light component in another predetermined direction perpendicular to that one predetermined direction is reflected thereon as the linearly polarized light component.
In a further mode of the first display device according to this invention, the liquid crystal panel is composed of a TN liquid crystal element, an STN liquid crystal element or an ECB (Electrically Controlled Birefringence) liquid crystal element.
According to this mode, it is possible to realize a high-quality liquid crystal display device offering bright reflective and transmissive displays without causing the positive-negative reversal in both displays. Incidentally, this STN liquid crystal element includes an STN liquid crystal element using a color compensation optical anisotropic material. Additionally, if used is a liquid crystal element, such as an ECB liquid crystal element, having a birefringence effect, it is possible to vary the color development from the light source.
The above-mentioned object of this invention is achievable by a second display device according to this invention comprising a liquid crystal panel in which a polarization axis is variable, first and second polarized light splitting plates located on both sides of the liquid crystal panel to interpose the liquid crystal panel therebetween, a reflecting layer located on the opposite side to the liquid crystal panel with respect to the second polarized light splitting plate, a light source, and a light guider located between the second polarized light splitting plate and the reflecting layer for guiding light from the light source through the second polarized light splitting plate to the liquid crystal panel and further for allowing transmission of light from the second polarized light splitting plate side and light from the reflecting layer side, with the light guider having an optical anisotropy which is so low that it hardly has influence on display chrominance non-uniformity or with the light guider having a constant optical axis direction.
With the second display device according to this invention, as mentioned above, the light guider has an optical anisotropy so low as to exert little influence on display chrominance non-uniformity or has a constant optical axis direction, and particularly in the reflective display, there is no need to step up light scattering through the use of, for example, a front scatterplate for the purpose of obscuring the display chrominance non-uniformity stemming from the optical anisotropy, and a bright good-looking display is attainable.
In a mode of the second display device according to this invention, there is additionally provided a front scatterplate located between the liquid crystal panel and the reflecting layer for forwardly scattering each of light from the reflecting layer side toward the liquid crystal panel side and light from the liquid crystal panel side toward the reflecting layer side.
According to this mode, as in the case of the above-described first display device according to this invention, in the reflective display, even if the distance from the liquid crystal panel to the reflecting layer is prolonged, neither double image nor bleeding in display stemming from the resultant parallax occurs, and the reflected light turns white. On the other hand, in the transmissive display, a bright display is obtainable through the use of light source light.
In another mode of the second display device according to this invention, the first polarized light splitting plate is a polarized light splitting plate which transmits, absorbs or reflects incident light in accordance with its polarized light component, while the second polarized light splitting plate is a polarized light splitting plate which transmits, absorbs or reflects incident light in accordance with its polarized light component.
According to this mode, it is possible to offer a bright display while conducting polarized light separation through the use of the first and second polarized light splitting plates each constructed with, for example, a polarizer.
In a further mode of the second display device according to this invention, the liquid crystal panel is composed of a TN liquid crystal element, an STN liquid crystal element or an ECB liquid crystal element.
According to this mode, it is possible to realize a high-quality liquid crystal display device providing bright reflective and transmissive displays without causing positive-negative reversal in both the displays.
In a further mode of the first display device according to this invention, additionally provided is coloring means interposed between the first polarized light splitting plate and the light guider.
According to this mode, not only in the reflective display relying on the external light but also in the transmissive display relying on light source lighting, the external light or the light source light passes through the coloring means, thereby accomplishing a color display. Particularly in the reflective display, the external light changed in polarized state by passing through the first polarized light splitting plate, the liquid crystal panel and the second polarized light splitting plate and colored by the coloring means is once returned to white scattering light by means of the front scatterplate, and then is reflected on the reflecting layer to penetrate the first polarized light splitting plate, the liquid crystal panel and the second polarized light splitting plate through the reflecting layer so that a change of its polarized state takes place, and again colored by the coloring means, thereafter being outputted from the first polarizing means side. Accordingly, even if the external light component passes through different coloring areas before and after the reflection, since the external light colored before the reflection is once returned to white scattering light, finally the color bleeding due to the external light (reflected light) colored after the reflection disappears substantially on the display image, thus achieving a bright good-looking color display.
In this mode, it is also acceptable that the coloring means is constructed with a color filter.
With this construction, the external light or the light source light is colored by the color filter so that a color display takes place in the reflective display and in the transmissive display. Among the coloring means, there are a light selection reflecting layer using a light interference filter, a hologram, a cholesteric liquid crystal or the like, a phase contrast layer, and others. However, from an easy-manufacturing point of view, a color filter using a dye or a pigment is most preferable.
In addition, with this construction, it is also possible that the aforesaid color filter is composed of three colors: a red-based color, a green-based color and a blue-based color.
According to this mode, a multicolor display and further a full-color display becomes possible.
Still additionally, in this case, the three-color filter can also be made so that its average transmittance ratio is in a range of 30% to 80%.
According to this mode, the average transmittance radio Ym of the three-color filter is expressed as:
Ym=(YR+YG+YB)/3xe2x80x83xe2x80x83(1)
where YR, YG and YB represent the transmittance ratios of the red-based color, the green-based color and the blue-based color, respectively.
Thus, when this average transmittance ratio Ym is set in the range of 30% to 80%, it is possible to provide a bright color display in the reflective display and to offer a non-fade-out color display in the transmissive display.
In a further mode of the second display device according to this invention, coloring means is provided additionally in a state interposed between the first polarized light splitting plate and the light guider.
According to this mode, not only in the reflective display relying on the external light but also in the transmissive display relying on the light source lighting, the external light or the light source light passes through the coloring means to produce a color display. Particularly, in the light guider, since the optical anisotropy is so low as to exert little influence on display chrominance non-uniformity or the optical axis direction is constant, a bright good-looking color display is attainable.
The above-mentioned object of this invention is also achievable by a first electronic apparatus incorporating the above-described first display device (including the above-described various modes) according to this invention.
According to the first electronic apparatus, because it is equipped with the above-described first display device according to this invention, in the reflective display, double image or bleeding is reducible, thereby enabling a bright good-looking monochrome or color display. In the transmissive display, a bright monochrome or color display is feasible.
The above-mentioned object of this invention is also achievable by a second electronic apparatus incorporating the above-described second display device (including the above-described various modes) according to this invention.
According to the second electronic apparatus, because it is equipped with the above-described second display device according to this invention, particularly in the reflective display, there is no need to increase the light scattering, for example, through the use of a front scatterplate for the purpose of obscuring the display chrominance non-uniformity stemming from the optical anisotropy, and a bright good-looking monochrome or color display is feasible.
The above-mentioned object of this invention is also achievable by a light guider for a first display device in which the optical anisotropy is so low in a plane as to exert little influence on display chrominance non-uniformity when used for a display device.
Alternatively, the above-mentioned object of this invention is also achievable by a light guider for a second display device, whose optical axis direction is a constant direction.
That is, when the light guide according to this invention for the first or second display device is used as the light guider in the above-described first or second display device according to this invention, as stated above, particularly in the reflective display, there is no need to step up the light scattering, for example, through the use of a front scatterplate for obscuring the display chrominance non-uniformity caused by the optical anisotropy, and a bright good-looking display is obtainable.
In this connection, in such a conventional art as shown in FIG. 22, since the reflecting plate is closer to the liquid crystal panel than the light guider, the optical anisotropy in the light guide basically exerts no influence on the display chrominance non-uniformity. For this reason, in the case of the conventional light guider, for the production thereof, no consideration has been given to the magnitude of its optical anisotropy or its optical axis direction. In consequence, in the conventional light guider, the optical anisotropy is so high as to exert influence on the display chrominance non-uniformity or the optical axis direction is not arranged in a constant direction. Accordingly, if the conventional light guider is built in such a construction as this invention in which a reflecting plate is on the remote side from a liquid crystal panel than a light guider, it is impracticable because display chrominance non-uniformity occurs.
Incidentally, when the above-described display devices according to this invention are constructed as a display device based on all well-known addressing systems such as a passive matrix system, an active-matrix system using TFTs (Thin Film Transistors) or TFDs (Thin Film Diodes) and a segment system, bright reflective and transmissive displays are also realizable.
Furthermore, in addition to the above-mentioned reflecting polarizer, the third polarized light splitting plate in the display device according to this invention accepts, for example, a combination of a cholesteric liquid crystal layer and a (xc2xc) xcex plate, an element designed to perform separation into reflected polarized light and transmitting polarized light utilizing an angle of polarization (SlD 92 DlGEST p427-429), an element using a hologram, a device disclosed in International Application published (International Application Publication: WO95/27819 and WO95/17692), and others. Incidentally, these various types of polarized light splitters are similarly available in place of the reflecting polarizer for each of embodiments which will be described later. Moreover, as each of the first and second polarized light splitting plates in the display devices according to this invention, in addition to the above-mentioned polarizer, it is also possible to employ various types of polarized light splitting plates.
The operations and other advantages of this invention will become apparent from the following description of embodiments.